Hard disk drives (HDD) are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model includes a storage disk or hard disk that spins at a designed rotational speed. An actuator arm with a suspended slider is utilized to reach out over the disk. The slider is coupled with a suspension that supports both the body of the slider and a head assembly that has a magnetic read/write transducer or head or heads for reading/writing information to or from a location on the disk. The complete head assembly, e.g., the suspension, slider, and head, is called a head gimbal assembly (HGA).
A typical HDD uses the actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read from the location. Within most HDDs, the magnetic read/write head is mounted on a slider. The slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive. The slider is aerodynamically shaped to establish an air lubrication film in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
The reading or writing of data is performed in accordance with a write command and a read command transferred from a host system. The hard disk drive re-orders a command queue as one of the performance improving techniques. That is, the command queue of write commands and read commands transferred sequentially from the host system is re-ordered so that the latency required to execute the writing or reading command may be minimized.
Recently some disk drives are being filled with low-density gases other than air (i.e., helium) to enhance their performance. The lower density gas can reduce the aerodynamic drag between the disks and their read/write heads. This reduced drag can, in turn, reduce arm and suspension flutter and actuator buffeting. This reduced drag can also result in a reduction in power requirements for the spindle motor. The lower density gas also is more effective than air for conducting away heat generated during operation of the disk drive.
Unfortunately, in spite of the advantages associated with the low-density gas fill, these gas filled disk drives have associated problems that have impacted their commercial success. These problems include the leakage of the gas from the disk drives over time. Furthermore, since the gas molecules of helium are the smallest known to man other than hydrogen, the diffusion rate through solids is high and virtually impossible to achieve perfect sealing of the disk drive. But since fundamental performance of the disk file, such as magnetic fly-height, servo tracking following, depend on the environment being nearly pure helium (at least (90%-95%), a means of detecting the helium concentration before performance degradation becomes critical and highly desirable.
However, no low cost helium sensing and feedback solution exists today. Thus a low cost solution to monitor the helium content of seal disk files is highly desirable.